This invention relates generally to systems for rigidly mounting objects on a support surface, and, more particularly, to mounting systems that isolate the mounted object from any forces caused by limited expansion or contraction of the support surface.
Mounting systems of this kind are particularly useful in mounting objects such as the microwave cavity of a hydrogen maser atomic clock in a cylindrical vacuum chamber. Successful operation of such a clock requires that its microwave cavity be tuned to a frequency that will precisely match the transition frequency of the hydrogen atom. Since the frequency of the microwave cavity is directly related to its dimensions, once tuned, the cavity dimensions must be held constant. It is, therefore, usually essential that forces acting on the cavity, e.g., the forces holding it in place, remain fixed. This requirement for fixed forces has proven generally difficult to meet in the past, because the dimensions of the vacuum chamber in which the microwave cavity is located are, themselves, usually subject to substantial changes due to temperature and pressure variations. Both the length and the radius of the vacuum chamber can frequently vary, to at least a limited extent. The mounting for the microwave cavity must permit this limited expansion and contraction of the vacuum chamber's dimensions, without changing the forces applied to the cavity.
One known prior structure for mechanically mounting a microwave cavity preloads the cavity in compression between the circular end plates of the vacuum chamber using a series of Bellville springs. These springs, when appropriately dimensioned, have a characteristic in which they can accommodate a range of deflection without changing their compressive load. The length of the vacuum chamber can thereby expand or contract, within the limits of the Bellville springs' flat region, without changing the compressive load on the cavity. Radial expansion or contraction of the vacuum chamber is prevented from inducing variable loads on the cavity by placing ball bearings in radial slots between the pre-compressed stack of Bellville springs and the vacuum chamber's end plates.
The Bellville spring and ball bearing structures described above function effectively in isolating the microwave cavity from the effects of any uniform expansion or contraction of the surrounding vacuum chamber. However, this structure has not proven to be entirely satisfactory. It has required the use of a large number of individual parts, including rings, bearings and Bellville springs, and it has required a very exact pre-compression load, which complicates its assembly and requires special tooling in the form of loading jacks to facilitate chamber closure.
It should, therefore, be appreciated that there is a need for an effective, yet less complex, constant force suspension system that isolates a mounted object from any forces caused by limited expansion or contraction of a support surface. The present invention fulfills this need.